This application claims the benefit of a priority under 35 USC 119 to French Patent Application No. 0104771 filed Apr. 9, 2001, the entire contents of which are incorporated by reference.
This invention is directed to the reconstruction of a three-dimensional image of an object from a set of two-dimensional projected images of the object, obtained for different positions of a means for acquiring an image, for example, by a camera, around the object.
The invention is of interest to the field of medical diagnostic imaging, in which reconstruction of the internal structures of an object, such as a patient, under examination is undertaken. In particular, the invention is applicable to the reconstruction of angiographic images, that is, obtaining images of vascular systems opacified by injection of a contrast medium.
In the field of medical diagnostic imaging, two-dimensional projected images of the object, for example, a patient""s abdomen, are generally obtained by rotation of an X-ray camera around the object. In an abdominal imaging application, peristalsis is known to cause defects in the reconstructed three-dimensional images. Those defects are due to the displacement of gas bubbles between the acquisition of so-called mask images, that is, in which no contrast medium has been injected, and the acquisition of opacified images. In other words, this produces white and black regions in the subtracted images. This phenomenon is particularly disturbing for three-dimensional reconstructions from subtracted projected images, because six to ten seconds can elapse between acquisition of the series of mask images and acquisition of the corresponding series of opacified images. The first negative effect of those defects is to disturb display of the reconstructed image by reason of their superposition on the vessels in three-dimensional images. As a result, the user removes the superposition manually by using, for example, an electronic scalpel. Another undesirable effect is produced when a multiresolution approach is used for reconstruction of the three-dimensional image. In that case, the signal comprises a large quantity of voxels and can lead to the suppression of some small vessels of the region which is reconstructed at high resolution.
The invention is directed to a reduction, preferably automatically, and even a total suppression of such defects in three-dimensional image reconstruction, particularly in abdominal angiographic images.
An embodiment of the invention is a method reconstruction of a three-dimensional radiographic image of an object, comprising:
(a) acquisition of a first series of projected two-dimensional mask images of the object obtained for different positions of a means for image acquisition, e.g. a camera, around the object;
(b) acquisition of a second series of opacified projected two-dimensional images of the object obtained at the same positions of the camera around the object;
(c) elaborating a third series of subtracted projected two-dimensional images respectively obtained from the first and second series of images;
(d) reconstruction of a subtracted three-dimensional image from the third series of images and from an analytical algorithm of image reconstruction;
(e) reconstruction of a three-dimensional mask image from a first series of images and from an analytical algorithm of image reconstruction;
(f) identification of defects in the three-dimensional mask image; and
(g) elimination of the corresponding voxels in the three-dimensional subtracted image.
According to one embodiment of the invention, the elimination of voxels entails resetting the intensity value.
According to another embodiment of the invention, the two three-dimensional image reconstructions are carried out at a first resolution, for example, a low resolution. A region of interest is then selected in the three-dimensional subtracted image and a new three-dimensional reconstruction is made of the region of interest alone, with a second resolution higher than the first resolution.
The invention is also directed to a radiographic apparatus for reconstructing a three-dimensional radiographic image of an object, comprising:
(a) means for acquiring images, such as a camera capable of rotating around the object;
(b) means for acquiring a first series of projected two-dimensional mask images of the object obtained for different positions of the camera rotating around the object;
(c) means for acquiring a second series of opacified projected two-dimensional images of the object obtained at the same positions of the camera around the object;
(d) means for elaborating a third series of subtracted projected two-dimensional images respectively obtained from the first and second series of images;
(e) means for reconstructing a subtracted three-dimensional image from the third series of images and from an analytical algorithm of image reconstruction;
(f) means for reconstruction of a three-dimensional mask image from the first series of images and from an analytical algorithm of image reconstruction;
(g) means for identifying defects in the three-dimensional mask image; and
(h) means for post-treatment for eliminating the corresponding voxels in the subtracted three-dimensional image.